Ferguson rock slide buries California State Highway near Yosemite National Park |
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| Authors: | Edwin L Harp Mark E Reid Jonathan W Godt Jerome V DeGraff Alan J Gallegos |
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| Institution: | (1) U.S. Geological Survey, Denver, Colorado, USA;(2) U.S. Geological Survey, Menlo Park, California, USA;(3) U.S. Forest Service, Vallejo, USA |
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| Abstract: | During spring 2006, talus from the toe area of a rock-block slide of about 800,000 m3 buried California State Highway 140, one of the main routes into heavily-visited Yosemite National Park, USA. Closure of
the highway for 92 days caused business losses of about 4.8 million USD. The rock slide, composed of slate and phyllite, moved
slowly downslope from April to June 2006, creating a fresh head scarp with 9–12 m of displacement. Movement of the main rock
slide, a re-activation of an older slide, was triggered by an exceptionally wet spring 2006, following a very wet spring 2005.
As of autumn 2006, most of the main slide appeared to be at rest, although rocks occasionally continued to fall from steep,
fractured rock masses at the toe area of the slide. Future behavior of the slide is difficult to predict, but possible scenarios
range from continued scattered rock fall to complete rapid failure of the entire mass. Although unlikely except under very
destabilizing circumstances, a worst-case, rapid failure of the entire rock slide could extend across the Merced River, damming
the river and creating a reservoir. As a temporary measure, traffic has been rerouted to the opposite side of the Merced River
at about the same elevation as the buried section of Highway 140. A state-of-the-art monitoring system has been installed
to detect movement in the steep talus slope, movement of the main slide mass, local strong ground motion from regional earthquakes,
and sudden changes in stream levels, possibly indicating damming of the river by slide material. |
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| Keywords: | Rock slide Yosemite National Park Monitoring GPS data Hazard |
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